Quality control of radiotherapy simulators

Abstract

Introduction

A radiotherapy simulator makes it possible to verify a radiotherapy treatment plan before starting treatment. The aim of this work was to evaluate the parameters of radiotherapy simulators affecting the precision of simulation.

Material and methods

A test protocol has been prepared based on appropriate IEC norms and the methodology used by service engineers, as well as on previous work undertaken at the Medical Physics Department. Two radiotherapy simulators (Varian Ximatron and Oldelft Simulix) have been regularly tested for a period of over one year.

Results

Tests have shown that on both simulators, precision of laser centrators (light beams indicating the isocenter), field size and telemeter (light scale indicating the source-to-skin distance) varies over time, which in some situations could lead to significant inaccuracies in simulations. Inaccuracies observed during the tests were, in most cases, not noticed by the operators. Usually, appropriate adjustments can only be made by service engineers. Other parameters affecting the geometrical precision of simulations have proved to be stable. Evaluation of image quality and X-ray beam parameters did not reveal any significant changes over a one-year period.

Conclusions

Mechanical parameters of radiotherapy simulators need to be tested regularly, with precision of laser centrators, field size settingsand telemeter readings requiring special attention.